Apparatus, system, and method for controlling a desired torque output

ABSTRACT

Apparatus, system, and method for controlling a desired torque output on a hydromechanical transmission. Controlling torque output of a hydromechanical transmission provides improved operator feel and control. A control module determines a desired torque output and determines a pressure necessary to influence the displacement of the variable displacement pump to output the desired torque output. A pressure-controlling valve applies that amount of pressure to an actuator, which moves in response thereto, to change the displacement of the variable displacement pump. When the motor speed changes, the control module adjusts the pressure applied to the actuator to provide the desired torque output.

TECHNICAL FIELD

The present invention relates to transmission controls, and morespecifically to controlling a desired torque output from ahydromechanical transmission.

BACKGROUND

Hydromechanical, split torque, or parallel path powertrains provide manyadvantages over the typical mechanical transmissions used inearth-working machines, such as tractors, bulldozers, and wheel loaders.Specifically, hydromechanical transmissions provide continuous speedcontrol, control of acceleration and deceleration, and management ofengine speed with fewer losses.

Current industry practice with hydromechanical transmissions is tocontrol speed by controlling pump displacement. This practice requires aservo-feedback control on a pump actuator to force the pump actuator toa specific position. Industry has had a measure of success with speedcontrol systems in the agricultural industry but no known successes inthe earth-moving industry. The lack of force (torque) control put theearth-working machines with hydromechanical powertrains at adisadvantage when compared to conventional powertrains, particularlywhen the machine was pushing against massive objects, or digging.Similarly, it was found that because earth-working machines are oftenemployed on rapidly changing surface conditions and compromisedstability, it was inherently harder to make smooth speed transitionswith the traditional speed control system.

One type of system for controlling speed is discussed in U.S. Pat. No6,684,636 to Smith. Smith teaches a method for controlling speed usingan electrical signal applied to a solenoid to change the pump'sdisplacement. On generally level surfaces, this method has beensuccessful, however, as discussed above, on uneven surfaces, anoperator, or machine experiences undesirable accelerations as thecontrols hunt for the desired speed.

The inability to determine the correct pump displacement under rapidlychanging surface conditions has resulted in the unsuccessful use of thespeed control system in the earth-moving industry. Any error in thedisplacement showed up as lugs and lurches and generally unfamiliarmachine behavior when compared to the precedent established by pastgenerations of successful earthmoving machines.

The present invention is directed to overcoming one or more of theproblems as set forth above.

SUMMARY OF THE INVENTION

In one aspect, an apparatus for controlling a desired torque output froma hydromechanical transmission. The apparatus comprises a control moduleconfigured to determine the desired torque and to determine an amount ofpressure necessary to influence the displacement of a variabledisplacement pump to output the desired torque.

In another aspect, a hydromechanical transmission for outputting adesired torque is provided. The hydromechanical transmission comprises avariable displacement pump drivingly connected to a suitable outputproducing device such as an internal combustion engine, a fixeddisplacement motor drivingly connected to the variable displacementpump, a gear system, an actuator, and a control module. The actuator isconfigured to influence displacement of the variable displacement pumpand the control module is configured to determine the desired torque andto determine an amount of pressure necessary to influence the actuatorto adjust the displacement of the variable displacement pump to outputthe desired torque.

In another aspect, a method for controlling a desired torque output froma hydromechanical transmission is provided. The method includes thesteps of determining the desired torque and outputting the desiredtorque from a motor of the hydromechanical transmission.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate exemplary embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention. In the drawings,

FIG. 1 illustrates a schematic for controlling torque output from amotor on a hydromechanical transmission;

FIG. 2 illustrates a schematic of an optional embodiment for controllingtorque output from a motor on a hydromechanical transmission;

FIG. 3 illustrates a schematic of another optional embodiment forcontrolling torque output from a motor on a hydromechanicaltransmission;

FIG. 4 illustrates a schematic of a further optional embodiment forcontrolling torque output from a motor on a hydromechanicaltransmission;

FIG. 5 illustrates a schematic for controlling torque output includingoptional sensors; and

FIG. 6 illustrates an actuator map for determining an actuator pressuredifference to effectuate a desired displacement of a variabledisplacement pump.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments of the invention,examples of which are illustrated in the accompanying drawing.

Referring to FIG. 1, a schematic for controlling torque output from ahydromechanical transmission 10 is shown. The hydromechanicaltransmission 10 comprises a gear system 12, a hydrostatic unit 16, aninput module 18, a control module 20, an actuator 22, and a valve system24.

The gear system, such as a transmission, 12 typically outputs to atraction device (not shown) on an earth-working machine. The tractiondevice may include wheels located on each side of the earth-workingmachine. Alternatively, the traction device may include tracks, belts,or other driven traction implements. Preferably, an internal arrangementof the gear system 12 is a power split, a hydromechanical arrangement ofthe input coupled type, or a variable unit driven solely by an input,with one or more shiftable ranges. Other arrangements, such as outputand series coupled, are also envisioned.

The hydromechanical transmission 10 connects to an engine 14, which maybe any type of output producing device, such as an internal combustionengine, gas or diesel, a motor, pump, or generator and motor. The engine14 provides rotational energy to the hydrostatic unit 16 as well as thegear system 12.

The hydrostatic unit 16 comprises at least two rotating groups. Therotating groups include a variable displacement pump 26 and a fixeddisplacement motor 28, however the rotating groups may both be variabledisplacement. The variable displacement pump 26 fluidly drives the fixeddisplacement motor 28 to output rotational energy to the gear system 12.The hydrostatic unit 16 may be axial piston, bent axis, or other knownconfiguration. Similarly, the hydrostatic unit 16 may be arranged in a“U”, inline, or other known arrangement.

The input module 18 receives commands, or instructions, from a commandsource and transmits the commands to the control module 20 to operatethe earth-working machine according to the received commands. The inputmodule 18 may be a dial, a keyboard, an interactive display, electricalbuttons, switches and pedals, or known programming technique. Thereceived commands may be data identifying a desired input, predeterminedcriteria, a particular condition, or established parameters entered intothe input module 18. The commands may be preprogrammed into the controlmodule 20 to perform according to predetermined criteria and/orparameters, under predetermined conditions. The command source may be anoperator, such as a human being, or a set of code, software, orcircuitry configured to perform a particular function.

The control module 20 communicates with the input module 18, first andsecond speed sensors 30 and 32, a resolver 33, and the valve system 24.The control module 20 receives command input from the input module 18and determines what motor torque output is desired to provide thedesired machine response. Other sensors may be added as necessary toprovide additional feedback or system information.

It is noted that a module, such as the input module 18 and the controlmodule 20, may be implemented as a hardware circuit comprising customVLSI circuits or gate arrays, off-the-shelf semiconductors such as logicchips, transistors, or other discrete components. A module may also beimplemented in programmable hardware devices such as field programmablegate arrays, programmable array logic, programmable logic devices or thelike. Modules may also be implemented in software for execution byvarious types of processors. An identified module of executable codemay, for instance, comprise one or more physical or logical blocks ofcomputer instructions, which may, for instance, be organized as anobject, procedure, or function. Nevertheless, the executables of anidentified module need not be physically located together, but maycomprise disparate instructions stored in different locations which,when joined logically together, comprise the module and achieve thestated purpose for the module.

The control module 20 controls the actuator 22, which influences thedisplacement of the variable displacement pump 26. The actuator 22comprises a piston 34 centrally located in a cylinder 36. A pressuredifferential between a first side 38 and a second side 40 of thecylinder 36 effectuates a desired displacement of the variabledisplacement pump 26. Alternatively, as illustrated in FIG. 2, theactuator 22 may include spring force and control pressure 45 on one sideof the actuator 22 and supply pressure 46 on the other. In yet anotherembodiment, illustrated in FIG. 3, the actuator 22 may include controlpressure 45 on one side and spring force on the other. Alternatively,the actuator 22 may comprise two single acting cylinders (not shown) ofequal or different areas, each configured to receive pressurized fluidfrom the pressure controlling valves 47 and 48. One skilled in the artwill realize that the actuator 22 may be controlled by a variety offorces in a variety of ways.

Referring back to FIG. 1, the actuator 22 includes actuator springs 42and 44 configured to produce a centering force proportional to position,without discontinuity, throughout the entire range of displacement.

It is noted that, for conventional hydrostatic applications, zerodisplacement means zero output speed. Historically pumps have centeringsprings arranged to provide a large force discontinuity precisely atzero displacement that return the pump to zero displacement under anycondition. This characteristic is very useful for conventionalhydrostatics but it limits their ability to manage directional shifts.For hydromechanical applications in general, the zero displacement/angleposition holds no special significance whatsoever and moving smoothlythrough the zero displacement/angle is highly preferred. As a result,eliminating the springs altogether would be desirable. However theinertia of the pump pistons tend to stroke the pump away from zerodisplacement. Special speed matching conditions within the gear systemrequire enough centering spring force to overcome the piston inertia.

The valve system 24 adjusts the pressure acting on the actuator 22according to signals from the control module 20. The valve system 24includes first and second pressure controlling valves 47 and 48. Thefirst pressure-controlling valve 47 communicably connects to the controlmodule 20 and the first side 38 of the actuator 22, and the secondpressure-controlling valve 48 communicably connects to the controlmodule 20 and the second side 40 of the actuator 22. The first andsecond pressure controlling valves 47 and 48 supply known pressures as afunction of command input from control module 20. In another embodiment,illustrated in FIG. 4, the valve system 24 comprises a singleelectro-hydraulic valve 49 with a pressure differential output.

FIG. 5 illustrates locations of optional sensors according to oneembodiment of the present invention. Pressure sensors 50 may be added tofirst and second pressure controlling valve and outlets to monitoractual pressures. The sensors 50 communicate with the control module 20to provide information to control valve flow losses, valve-to-valvevariations, and valve nonlinearities. Pressure sensors 52 may also beadded to the hydrostatic unit 16 to reduce the need for pump mapping andprovide more accurate pressure limiting. The additional sensorarrangements improve diagnostic and error detection functions.

Referring to FIG. 6, a map for determining variable displacementactuator force is shown. The illustrated map shows actuator force(Actuator DeltaP) for a single input speed of 1,800 revolutions perminute to effectuate an effective displacement of the variabledisplacement pump 26 to output a desired torque at an existing motorspeed. The control module 20 manages Actuator DeltaP (psi) via the valvesystem 24.

The map relates variable displacement actuator force to desired outputtorque, variable displacement pump speed and normalized motor speed.Variable displacement actuator force is a function of circuit pressure,variable displacement pump shaft speed, and variable displacement pumpdisplacement angle. Circuit pressure also relates to motor torquethrough its fixed hydraulic displacement. Fixed displacement motortorque is a function of output torque through mechanical reductions inthe gear system 12. Variable displacement pump speed is known from thefirst speed sensor 30. Variable displacement pump displacement angle isgenerally proportional to normalized motor speed, which is the ratio offixed displacement motor speed to variable displacement pump speed.Normalized motor speed is calculated within the control module 20 withinput from the first and second speed sensors 30 and 32.

The control module 20 refers to the map to determine the Actuator DeltaP(or variable displacement actuator force) to influence the position ofthe actuator 22. Upon determination of the proper Actuator DeltaP, thevalve system 24 effectuates the proper force against the actuator 22 sothat the actuator 22, or force against the actuator 22, exerts thatamount of force on the variable displacement pump 26.

It is noted that for different input speeds a different mapping surfaceis used. It is further noted that for systems with multiple pumps, eachpump may require its own map.

INDUSTRIAL APPLICABILITY

In operation, on earth-working machines, the engine 14 outputs to thegear system 12 and the hydraulic unit 16, which also outputs to the gearsystem 12. In combination, the hydraulic unit 16 and gear system 12 forma hydromechanical transmission.

To effectuate the desired machine response and to output the desiredtorque, the control module 20 receives input information from thecommand source and input module 18. The command source enters thepredetermined criteria, parameters, or conditions into the input module18. The control module 20 processes the input information to determinethe desired torque for the given input, determines input speed,determines normalized motor speed, and refers to the map to determinehow much actuator force is necessary to effectuate the desireddisplacement of the variable displacement pump 26. In response to asignal indicative of the required actuator force, the first and secondpressure controlling valves 47 and 48 cooperate to provide a pressure tothe actuator to produce a force against the piston to influencedisplacement of the variable displacement pump 26. The displacement ofthe variable displacement pump 26 adjusts accordingly to produce apredetermined pressure difference in the hydrostatic circuit between thepump 26 and the motor 28. The motor 28 outputs a torque as a function ofthe pressure difference in the hydrostatic circuit.

Sensors 50, 52, and 56 are positioned throughout the hydraulic circuitto monitor actual pressures and speeds. The information obtained fromthe sensors 50, 52, 54, and 56 is transmitted to the control module 20,which adjusts the system as necessary to maintain the desired torque.

As resistance to machine movement increases, for example, as the machinepushes against a pile of dirt or rock, or as the machine climbs a hill,the speed of the motor changes. Consequently, the normalized motor speedchanges. The control module 20 recognizes the change, refers to the mapand determines a new actuator DeltaP necessary for maintaining thedesired torque. Subsequently, the control module 20 sends a signal tothe pressure controlling valves 47 and 48 to adjust the pressures withinthe actuator according to the determined actuator DeltaP. The pressurecontrolling valves provide the determined pressure (DeltaP) to theactuator 22, which moves the piston 34 to effectuate a correspondingchange in the displacement of the variable displacement pump. Thepressure difference within the hydrostatic circuit adjusts accordingly,which causes the motor to output the desired torque.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the disclosed system forcontrolling torque output without departing from the scope or spirit ofthe invention. Other embodiments of the invention will be apparent tothose skilled in the art from consideration of the specification andpractice of the invention disclosed herein. It is intended that thespecification and examples be considered as exemplary only.

1. An apparatus for controlling a desired torque output from ahydromechanical transmission, comprising a control module configured todetermine the desired torque and to determine an amount of pressurenecessary to influence the displacement of a variable displacement pumpto output the desired torque.
 2. The apparatus of claim 1, wherein thecontrol module is configured to send a signal indicative of thedetermined pressure to at least one pressure controlling valve, andwherein the at least one pressure controlling valve operates to providethat amount of pressure to an actuator, which influences thedisplacement of the variable displacement pump accordingly.
 3. Theapparatus of claim 1, wherein the control module refers to a map todetermine the amount of pressure necessary to influence the displacementof the variable displacement pump.
 4. The apparatus of claim 3, whereinthe map relates desired output torque and normalized motor speed to thenecessary pressure for influencing the actuator.
 5. The apparatus ofclaim 1, wherein the control module determines the desired torque from aposition sensor of an input device.
 6. The apparatus of claim 5, whereinthe input device is a throttle control device.
 7. A hydromechanicaltransmission for outputting a desired torque, comprising: a variabledisplacement pump drivingly connected to an engine; a motor drivinglyconnected to the variable displacement pump; an actuator configured toinfluence displacement of the variable displacement pump; and a controlmodule configured to determine the desired torque and to determine anamount of pressure necessary to influence the actuator to adjust thedisplacement of a variable displacement pump to output the desiredtorque.
 8. The transmission of claim 7, further comprising a pressurecontrolling device communicably coupled to the control module and theactuator and configured to adjust the pressure in the actuator inresponse to a signal from the control module.
 9. The transmission ofclaim 8, wherein the pressure controlling includes a singleelectro-hydraulic valve configured to provide a pressure differentialoutput.
 10. The transmission of claim 8, wherein the pressurecontrolling device is configured to control pressure on one side of theactuator, which includes spring force on the other
 11. The transmissionof claim 8, wherein the pressure controlling means comprises: a firstpressure controlling valve coupled to the control module and a firstside of the actuator, and configured to adjust a pressure on a firstside of the actuator in response to a first signal; and a secondpressure-controlling valve coupled to the control module and a secondside of the actuator, configured to adjust a pressure on a second sideof the actuator in response to a second signal.
 12. The transmission ofclaim 7, further comprising: a resolver communicably coupled to thecontrol module and configured to provide circuit pressure between thevariable displacement pump and the motor.
 13. The transmission of claim7, further comprising: a first speed sensor positioned to provide aspeed of the variable displacement pump; and a second speed sensorpositioned to provide a speed of the motor.
 14. The transmission ofclaim 13, wherein the control module determines the actuator pressurenecessary to influence the displacement of the variable displacementpump with respect to the desired output torque and a determinednormalized motor speed.
 15. The transmission of claim 11, furthercomprising: a first pressure sensor connected to an output from thefirst pressure controlling valve; and a second pressure sensor connectedto an output from the second pressure-controlling valve.
 16. Thetransmission of claim 7, wherein the actuator comprises a cylinder and apiston, the piston being slidably located within the cylinder, whereinthe piston moves in response to a signal from the control module toinfluence the displacement of the variable displacement pump.
 17. Thesystem of claim 8, wherein the pressure controlling device comprises: apressure controlling valve communicably coupled to the control module,and a pressure line connected to one side of the actuator; and apressure line providing a supply pressure to an opposite side of theactuator.
 18. The transmission according to claim 17, wherein theactuator includes at least one spring acting against a piston of theactuator.
 19. A method for controlling a desired torque output from ahydromechanical transmission, comprising the steps of: determining thedesired torque; outputting the desired torque from a motor of thehydromechanical transmission.
 20. The method according to claim 19,after determining the desired torque, the steps of: determining anamount of pressure necessary to influence the displacement of a variabledisplacement pump to output the desired torque; and creating a forceagainst the an actuator of the variable displacement pump to effectuatea displacement of the variable displacement pump corresponding to thedesired torque output.
 21. The method of claim 20, wherein thedetermining the amount of pressure includes the step of determining anormalized motor speed.
 22. The method of claim 20, wherein the creatinga force step includes the steps of applying the determined amount ofpressure to an actuator to create the force.
 23. The method of claim 22,wherein the creating a force step includes the steps of controlling apressure on a first side of the actuator in response to a first signaland controlling a pressure on a second side of the actuator in responseto a second signal.
 24. The method of claim 22, wherein the creating aforce step includes the step of providing a pressure differentialbetween a first and second side of the actuator to move a piston withinthe actuator.